SB 618 
.M5 113 
1921a 
Copy 2 



JNITED STATES DEPARTMENT OF AGRICULTURE 

Sk 



Effi BULLETIN No. 942 ME 

>*\iUS? Contribution from the Bureau of Animal Industry %SlL>^ / iR^ 

/ ^-^ JOHN R. MOHLER, Chief S\^f r '^>mfU 



&JV 



Washington, D. C. 



PROFESSIONAL PAPER 



May 4, 1921 



POISONOUS PROPERTIES OF THE WHORLED 

MILKWEEDS ASCLEPIAS PUMILA AND 

A. VERTICILLATA VAR. GEYERL 

By C. Dwight JjIarsh, Physiologist in Charge of Investigations of Stock Poison- 
ing ly Plants, and A. B. Clawson, Physiologist, Pathological Division. 



PURPOSE OF PAPER. 

As stated in Department Bulletin 800, " The Whorled Milkweed 
(Asclepias galioides) as a Poisonous Plant'' (pp. 5 and 6), there are 
certain other species of whorled milkweed closely related to A. 
galioides. These species have a fairly wide distribution in the United 
States and it is a matter of considerable interest to know whether they 
have poisonous properties similar to those found in A. galioides. 
While hitherto these other species have not been examined experi- 
mentally, there has been good reason to suspect some of them of 
being connected with losses of livestock. 

Experimental work on two species, A. pumila and A. verticillata 
var. geyeri, has now demonstrated their toxic character, and also has 
brought out quite definitely the character of their action as compared 
with A. galioides. In this bulletin are summarized the results of the 
experimental work on these plants. The work accomplished indi- 
cates that A. pumila is about one-third as toxic as the very poisonous 
A. galioides, and A. verticillata var. geyeri is less poisonous, being 
about one-tenth as toxic as A. galioides. 

DESCRIPTION OF ASCLEPIAS PUMILA. 1 

Asclepias pumila (PI. I) may be called low whorled milkweed, or 
Great Plains whorled milkweed. -The stems, which are often 

1 In conformity with the cooperative arrangement between the Bureau of Plant Industry 
and the Bureau of Animal Industry in regard to investigations of poisonous plants, the 
material on which this paper is based was collected by W. W. Eggleston, Bureau of Plant 
Industry,, and the description of Asclepias pumila and that of A. verticillata var. geyeri, 
on page 10, were prepared by him. Mr. Eggleston has made a detailed study of the 
systematic position and distribution of these plants, which it is expected will be pub- 
lished later. 

25377° — 21 






2 BULLETIN 942, TJ. S. DEPARTMENT OF AGRICULTURE. 

branching, are 3 to 12 inches high, tufted, and puberulent. The 
main root is horizontal, branching, and produces adventitious buds. 
Figure 2 of Plate I shows plants growing from adventitious buds 
on the root. The leaves, which are 1 to 2 inches long, are sessile, nu- 
merous, crowded, and irregularly alternate to verticillate, linear- 
foliform, revolute, and scabrous-puberulent. The flowers are in 
terminal branching umbels, few to many flowered, with short pedun- 
cles, and are scabrous-puberulent. The greenish-white corolla has 
oblong lobes and white oblong hoods, which are hastate-sagittate in 
back view and shorter than the horn. The follicles are erect, puberu- 
lent and H to 3 inches long. The plant is found in adobe draws, in 




Fig. 1. — Distribution of Asclepias pumila. 

dry plains, and in foothills from southeastern Montana and south- 
western North Dakota to the Texas Panhandle and central New 
Mexico. It is most abundant on the plains of Colorado. 

Text figure 1 shows the distribution of the plant. Although it has 
a root system and seeds similar to Asclepias galioides, it has not 
spread widely. It usually is scattered in small patches in draws. 

The systematic position of Asclepias pumila is discussed in United 
States Department of Agriculture Bulletin 800, pages 5 and 6. 



EXPERIMENTAL WORK WITH A. PUMILA. 

All experimental work which was carried on in the summer of 
1919 was with sheep, and the material in all cases was administered 
by the balling gun. 



LIBRARY OF CONGRESS 
POGUMfcNTi* vol i«ION 

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^Gfr'S 






POISONOUS PROPERTIES OF THE WHORLED MILKWEED. 6 

The plant material used was collected in Yuma County, Colo. — a 
part of it in the town of Wray. The material was dried, but in the 
experimental work was estimated as green plant, 72 per cent being 
allowed for loss of weight in drying. 

The following table is a summarized account of the experiments. 
22 in number : 



Table 1. — Summary of feeding experiments with Asclepias pumila {air-dried 
plant fed with balling gun). 



Animal. 



Designa- 
tion. 



Weight. 



Sheep 532. 

Sheep 514. 
Sheep 539. 
Sheep 547. 
Sheep 546. 
Sheep 482. 
Sheep 486. 
Sheep 530. 
Sheep 536. 
Sheep 539. 
Sheep 552. 
Sheep 516. 

Sheep 547. 



Sheep 554. 
Sheep 546. 
Sheep 512. 
Sheep 520. 
Sheep 539. 
Sheep 516. 
Sheep 542. 
Sheep 519. 
Sheep 547. 



Pounds. 



Date of 
feeding. 



1919. 
July 23 



135 


July 


25 


99 


July 


26 


89.5 


Julv 


28 


100 


Julv 


29 


122.5 


Aug. 


1 


135 


Aug. 


5 


95 


Aug. 


8 


114 


Aug. 


11 


104 


Aug. 


15 


94.5 


Aug. 


L8 


81.5 


Aug. 


24 


95.5 


Aug. 


29 


104.5 


Sept. 


2 


101.5 


Sept. 


6 


124.5 


Sept. 


11 


102 


Sept. 


lo 


105. 75 


Sept. 


1, 


80.75 


Sept. 


19 


111.5 


Sept. 


23 


85 


Sept. 


2o 


99 


Sept 


27 





Weight 




of plant 




(esti- 




mated 


Part of plant 


as green 


used. 


plant) 




for 100 




pounds 

of 
animal. 






Pounds. 


Leaves and 


0.150 


stems. 




do 


.197 


do 


.295 


.....do 


.402 


do 


.787 


do 


.7^7 


do 


.827 


do 


.866 


do 


.866 


do 


.905 


do 


.984 


do 


.984 


do 


1.063 


do 


1.181 


do 


1.339 


do 


1.496 


do 


1.693 


do 


.7^7 


do 


1.850 


do 


1.968 


do 


2. 165 


do 


2.559 



Remedy 
used. 



None. 



do 

do 

do 

do 

....do 

do 

....do 

do 

do 

....do 

do 

Esenn and 
pilocar- 
pin. 

None 

do 

do 

do 

do 

do 

do 

do 

do 



Result. 



Not sick . 



do 

do 

do 

Symptoms. 
do 

Sick 

Symptoms. 

Somewhat sick 

Symptoms. 

Sick 

do 

do 



do 

do 

Symptoms. 

Sick 

Symptoms 

Sick 

do 

Died 

do 



Place and date of 
plant collection. 



Wray, Colo., July 5, 
1919. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 
Yuma County, Colo., 
Aug. 12, 1919. 

Do. 



Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 
Do. 



TYPICAL CASE OF SHEEP 547. 

Sheep 547 was a ewe which had been used for other experimental 
work earlier in the season, but was in good condition when on July 
28, 1919, she was selected for feeding with Asclepias pumila. At 
that time she weighed 8-1 pounds. At 3.10 p. m., 0.402 pound green 
weight of the plant per 100 pounds of animal was given by the ball- 
ing gun. This produced no effect. 

On August 29, at 6.04 p. m., the sheep was given, by the balling 
gun, 1.063 pounds of plant, green weight, per 100 pounds of animal. 
At this time she weighed 95.5 pounds. On August 30, at 7.25 a. m.. 
the pulse was 112 and weak, the respiration 12. rather deep, with 
somewhat forcible expirations. She was humped up, with the head 
held high, and showed weakness in the hind legs. Later in the day 



4 BULLETIN 942, IT. S. DEPARTMENT OF AGRICULTURE. 

she staggered when walking, appearing " stiff behind." During this 
day and August 31 her condition remained much the same. She was 
depressed, held the head high much of the time, and staggered or 
wabbled when walking. On September 1 the uncertain movement 
in walking had largely disappeared, but she was rather inactive. On 
September 2 she had apparently entirely recovered. There was no 
elevation of temperature during this sickness. 

This animal received several doses of eserin and pilocarpin, but 
apparently the remedy had no beneficial effect. 

On September 27 another experimental feeding was made, the 
sheep at this time weighing 99 pounds. She received 2.559 pounds, 
green weight, per 100 pounds of animal, between 3.20 and 3.50 p. m. 
On September 28, at 7.40 a, m., she stood with head held high and 
nose extended, was somewhat bloated, and unsteady on her feet, this 
latter characteristic being most marked in the hind legs. 

At 9.09 a. m. the pulse was weak, respiration irregular, and the 
animal staggered badly. This condition continued, the weakness and 
discomfort increasing. Plate II, figure 1, taken at 10.46 a. m., when 
she was somewhat salivated, illustrates the general condition. At 
11.15 a. m. she was found down and unable to rise. She went into a 
spasm at 11.21, with the head drawn toward the breast. Another 
spasm followed at 11.35, the head being first drawn down and then 
thrown back in the position of opisthotonos. 

The pulse at this time was rapid and weak and the respiration 
labored. Until about 6 p. m. there was an almost continuous series 
of spasms, the time between successive ones rarely being as much as 
5 minutes. At noon running movements appeared in connection 
with the spasms. The spasms were very violent for the most part, 
opisthotonos being very marked and sometimes the head was struck 
upon the ground with great violence. Plates II and III show some 
of the attitudes assumed between 11.36 a. m. and 1.45 p. m. 

About 6 p. m. the animal became comparatively quiet, and re- 
mained *so until 8.50 p. m., when a series of continuous spasms com- 
menced, which were terminated by death at 9.23 p. m. 

Most of the time the pulse was rapid and weak. The respiration 
varied, sometimes being very rapid, and at others slower and labored. 
Text figure 2 shows the curve of temperature. It will be noted that 
there were three high periods, the maximum, 109.6 F., being at the 
time of death. The low period between 6 and 8 p. m. is correlated 
with a time of comparative quiet, but this is not true of the 3 o'clock 
low, for the spasms were practically continuous during the after- 
noon. The immediate cause of death was respiratory paralysis. 

The autopsy was made immediately. There was clotted blood in 
the trachea and bronchi, and the lungs were congested. The stom- 



POISONOUS PROPERTIES OF THE WHORLED MILKWEED. 5 

achs appeared normal. There was some gas in the jejunum and 
ileum, and congestion in the posterior part of the ileum. The liver 
was pale and blotched, and the gall bladder was distended with gas. 
Tapeworms were present in the bile ducts and in the pancreatic duct. 
There were hemorrhagic spots on the surface of the thymus. The 
brain and spinal cord appeared normal. 

The results of microscopic examination of the tissues are given on 
pages 7 to 10. 

SYMPTOMS. 

The most prominent symptom in all the cases of poisoning was a 
weakness of the hind quarters of the animals, which resulted in a 
There was in most of the cases depression and in 



SEPT.27 
AM. I PM. 



SEPT.28 



PM. 



9 
HO 

'09 
108 
107 

l^/os 

\~ 

§/03 
102 
101 


















































































































































i 




























































1 


\ 


















































































A 






































































A 




i 


\ 




/ 


t 
































































y 




I 




I 


I 




































































\ 






















































































































































































5 

Q 








































































g 
































































99 
















1 











































































































































Fig. 2. — Temperature curve of Sheep u47. 

some evident trembling, but the staggering- was universally present 
and was particularly noticeable. This was not due in most cases to 
extreme weakness, for the animals could get about quite readily, but 
appeared in a gait which reminded one very much of a drunken man. 
This symptom of staggering was one which in some cases continued 
for several days. The pulse generally was weak and rapid, and the 
animals which were quite sick frequently accompanied the expira- 
tions with a grunt or a groan. In the cases which recovered there 
was no bloating, salivation, or spasm. It was quite noticeable in 
many of the cases that the animals when standing held the head 
high and the nose extended forward in a very characteristic fashion. 
In the animals which were fatally poisoned, in addition to the symp- 
toms already described, there was some bloating and salivation, and 



6 



BULLETIN 942, U. S. DEPARTMENT OF AGRICULTURE. 



they exhibited violent spasms, accompanied with running move- 
ments. The temperature in the two fatal cases, Sheep 519 and 547, 
ran for a period very high, reaching a maximum of 107° F. in Sheep 
519 and 109.6° F. in Sheep 517. In the spasms the latter animal 
threw itself at times in the opisthotonic position, and occasionally 
drew its head toward the thorax with a spasmodic motion. 

In comparing these symptoms with those shown by Asclepias 
galioides there is nearly a complete resemblance. The symptoms 
exhibited in the fatal case of one could not be distinguished from 
those seen in the other. In the cases of intoxication with recovery, 
no spasms appeared, and in this respect A. pumila differs from A. 
galioides. This, however, may be explained by the fact that ^4. 
pumila is much less toxic than A. galioides, and it may be supposed 
that in the cases of intoxication there was not enough of the poi- 
sonous principle to produce the spasmodic stage. 

TIME REQUIRED TO PRODUCE SYMPTOMS. 

The following table shows the time that elapsed after the feeding 
of A. pumila before symptoms appeared: 



Table 2. — Time elapsed after feeding A. pumila before appearance of symptoms. 





Quantity 




Time 




Quantity 




Time 




fed 




elapsed 




fed 




elapsed 


Animal. 


per 100 


Result. 


before 


Animal. 


per 100 


Result. 


before 




pounds of 




symptoms 




pounds of 




symptoms 




animal. 




appeared. 




animal. 




appeared. 




Pounds. 




Hrs. Mins. 




Pounds. 




Hrs. Mins. 


Sheep 546.. 


0.787 


Sick 


13 40 


Sheep 546... 


1.339 


Sick 


13 40 


Sheep 482.. 


.787 


...do 


30 15 


Sheep 512... 


1.496 


...do 


13 10 


Sheep 486.. 


.827 


...do 


12 37 


Sheep 520... 


1.693 


...do 


13 46 


Sheep 536.. 


.866 


...do 


16 50 


Sheep 539... 


0.787 


...do 


15 50 


Sheep 539.. 


.905 


...do 


16 — 


Sheep 51 6... 


1.85 


...do 


17 40 


Sheep 552.. 


.984 


...do 


15 45 


Sheep 542... 


1.968 


...do 


13 8 


Sheep 516.. 


.984 


...do 


21 — 


Sheep 519. . . 


2.165 


Died 


20 20 


Sheep 547.. 


1.063 


...do 


13 8 


Sheep 5 i 7... 


2.559 


...do 


15 50 


Sheep 554.. 


1.181 


...do 


14 13 











The average time of all cases shown in the table was 16 hours 17 
minutes. 

CONTINUATION OF SYMPTOMS. 

It was noticed in the experimental cases of poisoning with A. 
pumila that the symptoms in some cases continued for a long period 
of time. The following table shows these facts. This table was 
prepared by taking the time between the appearance of symptoms 
and the last time when symptoms were noted. The actual periods 
were probably somewhat greater than those in the table, for in most 
cases the first symptoms were noted in the morning, and the animals 
may have been sick earlier. It is probable, too, that the symptoms 
extended somewhat beyond the time the table would indicate. 



POISONOUS PROPERTIES OF THE WHORLED MILKWEED. 
Table 3. — A. pumila — Duration of sickness in cases of recovery. 



Designation of 
animal. 


Duration of symptoms. 


Designation of 
animal. 


Duration of symptoms. 


Sheep 546 


1 day. 

1 day. 

2 days 2\ hours. 
2 days 4 "hours. 
7 J hours. 

1 day 1 hour. 

1 day 17 hours. 

2 days 4* hours. 






Sheep 482 




3 aays 9^ hours. 


Sheep 4Sg 


Sheep 512 


Sheep 536 


Sheep 520 


1 day. 

1 day 8 hours. 

4 days. 

5 days. 


Sheep 539 


Sheep 539 




Sheep 516 - 

Sheep 512 


Sheep 516 











It will be noticed that the symptoms continued from a minimum of 
7£ hours to a maximum of 5 days. With the exception of Sheep 539 
the dosage was gradually increased in the order of the table. While 
there was no exact relation between the size of the dose and the dura- 
tion of the symptoms, in a very general way the greater doses caused 
the more prolonged symptoms. 

Of the two animals that died, death followed in Sheep 519 in 32 
hours, and in Sheep 547 in 38 hours. 

AUTOPSIES. 

The findings from the post-mortem examinations of the two cases 
that terminated in death were not very positive. In each case the 
animal was bloated and there was some gas in the alimentary canal. 
However, so far as appeared without microscopic examination, there 
were no clearly marked lesions in any of the organs. 

MICROSCOPIC CHANGES IN TISSUES OF SHEEP KILLED BY "ASCLEPIAS PUMILA." 

Liver. — The hepatic cells in the two fatal cases were swollen so as to 
crowd the blood largely out of the capillaries. Cloudy swelling was 
pronounced in the liver of Sheep 547, the cytoplasm of the hepatic 
cells being very granular and having a ground-glass appearance, 
which made it difficult to make out fine details. This condition was 
not so well advanced in Sheep 519. The blood in many veins con- 
tained much hemosiderin pigment, areas of granular material, pieces 
of degenerated hepatic cells, and sometimes portions of epithelium 
from the walls of the veins. Some of the veins were engorged, others 
not. The bile ducts were often catarrhal. The changes in the hepatic 
cells in both animals, especially in Sheep 547, were more pronounced 
than in the -4. galioides cases. 

Kidneys. — The changes were practically like those found in the 
A. galioides cases, consisting of areas of congestion and edema and a 
swollen and somewhat degenerated condition of the epithelium, par- 
ticularly in the convoluted tubules. In many tubules the lumina were 
practically filled by the swollen cells. Other cells were degenerated 
and partly disintegrated! Most nuclei stained well; a few stained 



8 BULLETIN 942, U. S. DEPARTMENT OF AGRICULTURE. 

very faintly, while others were wrinkled. In the congested areas there 
were deposits of hemosiderin pigment, much of it being in tubule 
epithelial cells. Apparently pronounced hemolysis occurred. 

Heart. — This tissue was mildly congested in some areas in Sheep 
547, and a few minute hemorrhages occurred. In both animals the 
cross-striated appearance was less pronounced than usual, especially 
in areas where the cytoplasm was more granular than normal. This 
was less marked than that found in some of the A. galioides cases, but 
was not materially different and probably was the result of excessive 
activity of the cardiac muscle. 

Lungs. — The sections of the lungs of Sheep 547 showed congestion ; 
those of Sheep 519 did not. In both cases, however, hemosiderin 
pigment was present and thrombi were found in the arteries. While 
these thrombi differed somewhat in detail their origin may have been 
and probably was the same. The fact that they were found in arteries 
indicates that they were embolic in nature and possibly originated in 
the liver. 

Thyroid. — The thyroid from each animal appeared to be normal 
except for a possible slight increase in connective tissue in Sheep 540, 
which had no connection with the A. yumila poisoning. In the A. 
galioides cases the thyroid tissue was congested. 

Thymus. — The thymus from Sheep 547 was the only one examined. 
It was severely congested and was hemorrhagic as well as edematous. 
The medullary portion of the lobules was especially full of blood. 
No changes of importance were noted in the lymphoid cells, though 
in places large cells with finely granular cytoplasm, apparently 
phagocytic in nature, were present. 

Nervous system. — The pronounced congestion noted in various 
parts of the nervous system in the A. galioides cases was absent in 
both the sheep poisoned by A. pimiila, though all portions examined 
were somewhat edematous. In the lumbar cord of each case, and in 
the cerebrum and the cerebellum of Sheep 519, a small amount of 
diapedesis of erythrocytes had occurred. The nerve cells of the 
medulla and spinal cord and the Purkinje cells of the cerebellum in 
both cases had undergone marked changes. The Purkinje cells of 
sheep poisoned with A. galioides were found to show marked, or in 
some cases, extreme fatigue effects. Changes in other nerve cells 
were apparently fatigue effects. 

Thrombi were found in the meninges and sometimes in the nervous 
tissue. Some of these contained fibrin, others appeared hyalin. 

Alimentary canal. — The only portion showing changes which may 
be considered due to the A. pumila was in the ileum and suggested 
the presence of an irritant. The ileum of Sheep 547 was mildly con- 
gested, and hemorrhages had occurred. In the mucosa was an ab- 
normal number of mononuclear leucocytes. A similar invasion, but 



Bui. 942, U. S. Dept. of Agriculture. 



Plate I. 




Fig. I.— Asclepias pumila. 




Fig. 2.— Asclepias pumila, Showing Plants Growing from 
Adventitious Buds on the Horizontal Root. 



Bui. 942, U. S. Dept. of Agriculture. 



Plate II. 




Fig. I.— Sheep 547, at 10.46 p. m. 
September 28. 



Fig. 2-Sheep 547, at 11.36 a. m. 
September 28. 




Fig. 3.— Sheep 547, at 11.39 a. m., 
September 28. 



Fig. 4.— Sheep 547, at 11.43 a. m. 
September 28. 




Fig. 5.— Sheep 547, at 11.51 a. m. 
September 28. 



Fig. 6.— Sheep 547, at 11.55 a. m. 
September 28. 



Bui. 942, U. S. Dept. of Agriculture. 



Plate III. 




Fig. i.-Sheep 547, at 12.03 p. m. 
September 28. 




FIG. 2.-SHEEP 547, AT 12.06 p. m. 
September 28. 




Fig. 3.-Sheep 547, AT 12.09 P. M. 
September 28. 




Fig. 4.— Sheep 547, at 1. 01 p. m. 
September 28. 




Fig. 5.— Sheep 547, at 1.09 p. m., 
September 28. 




FIG. 6.-Sheep 547, AT 1.45 P. M., 
September 28. 



POISONOUS PROPERTIES OF THE WHORLED MILKWEED. 



9 



of polymorphonuclear leucocytes, occurred in the mucosa of the 
ileum of Sheep 519. In some blood vessels thrombuslike areas oc- 
curred. 

Spleen. — This organ was not very abnormal, though the presence 
of considerable hemosiderin pigment indicated a possible congestion 
which had subsided. The edematous condition of the Malpighian 
corpuscles in the spleen of Sheep 547 indicated a possible congestion. 

While there was a marked similarity in the tissue changes to those 
in animals poisoned by A. galioides, there were certain slight differ- 
ences, mainly of degree. On the whole the findings in the two sheep 
examined agreed very well. 



TOXIC AND LETHAL DOSAGE. 



The following table shows the dosage, estimated as green plant, of 
A. purrdla, which resulted in sickness or death of the sheep. 

Table 4. — Dosages of A. pumila resulting in sickness or death. 





Quantity 






Quantity 






Quantity 






per 100 






per 100 






per 100 




Animal. 


pounds 

of 
animal. 


Result. 


Animal. 


pounds 

of 
animal. 


Result. 


Animal. 


pounds 

of 
animal. 


Result. 




Pounds. 






Pounds. 






Pounds. 




Sheep 546... 


0.787 


Sick. 


Sheep 516... 


0.984 


Sick. 


Sheep 539... 


0.787 


Sick. 


Sheep 482... 


.787 


Do. 


Sheep 547... 


1.063 


Do. 


I Sheep 516... 


1.85 


Do. 


Sheep 486... 


.827 


Do. 


Sheep 554... 


1.181 


Do. 


Sheep 542... 


1.968 


Do. 


Sheep 536. . . 


.866 


Do. 


Sheep 546... 


1.339 


Do. 


Sheep 519... 


2. 165 


Died. 


Sheep 539... 


.905 


Do. 


Sheep 512... 


1.496 


Do. 


Sheep 547... 


2.559 


Do. 


Sheep 552. . . 


.984 


Do. 


Sheep 520... 


1.693 


Do. 









It will be noticed that the smallest quantity which produced in- 
toxication was 0.787 pound per 100 pounds of animal. As shown 
in Table 1. the largest quantity fed without effect was 0.866 pound, 
to Sheep 530. In this case, however, there were possible symptoms. 
The smallest dose that produced death was 2.165 pounds per 100 
pounds of animal. It may be recalled that in all the A. pumila cases 
the whole plant was used. There are no data to determine the com- 
parative toxicity of different parts of the plant. 

With A. galioides the smallest quantity of the whole plant that 
produced symptoms was 0.22 pound, and this dosage resulted in 
death. In comparing the two plants it is evident that A. galioides is 
nearly 3.6 times as toxic as A. pumila. 

While, in the experiments with A. galioides, there was practically 
no difference between the toxic and lethal doses, in A. pumila it re- 
quired nearly three times the toxic dose to produce death. As com- 
pared with A. galioides the lethal dose of A. pumila was 9.84 times 
as great. Because of the small number of cases which were com- 
pared, these figures must not be considered as exact, but they give 
a general idea of the relative toxicity of the two plants. 



10 



BULLETIN 942, U. S. DEPARTMENT OF AGRICULTURE. 



EXPERIMENTAL WORK WITH A. VERTICILLATA VAR. GEYERI. 

A. verticillata, the whorled milkweed of the eastern part of the 
United States, is distributed throughout the Atlantic Plains and the 
Mississippi Valley. It differs materially from A. galioides, A. 
piimila, and J., mexicana in that it has long, fibrous roots and smooth 
pods. 

A. verticillata var. geyeri can be distinguished from the typical 
form by its numerous adventitious buds on the fibrous roots. These 
slender, fibrous budded roots are often long and horizontal and thus 
simulate the single strong horizontal roots of A. galioides, A. pumila, 
and A. mexicana. 

The material used in these experiments was collected at Missouri 
Valley, Iowa, on June 29, 1919. 

Thirteen feedings of this plant were made to sheep by the balling 
gun, resulting in two animals becoming sick and one other very sick. 
Three feedings with hay were made to a horse, with no result. 

The following table summarizes the experiments : 

Table 5. — Summary of feeding experiments with Asclepias verticillata var. 
geyeri {collected at Missouri Valley, Ioiva, and air dried). 



Animal. 



Designa- 
tion. 



Sheep 523 . 
Sheep 526 . 
Sheep 527 . 
Sheep 544 . 
Sheep 556 . 
Sheep 548 . 
Sheep 540 . 
Sheep 473 . 
Sheep 556 . 
Sheep 546 . 
Sheep 552 . 



Sheep 482 . 
Sheep 523 . 
Horse. 126 . 
Horse 126 . 
Horse 126 . 



Weight. 



Date of 
feeding. 



Pounds, 

82 

90.5 

82 

95.5 

98.5 
103 

97 

114.5 
106 

89.25 

97 



129 
92 
995 
995 
995 



1919. 
July 14 
July 15 
Julv 16 
July 17 
July 18 
July 19 
July 20 
July 21 
Aug. 12 
Aug. 22 
Sept. 20 



Sept. 23 
Sept. 25 

July 15-16 
Julv 1 

Julv 18-21 



Method of 
feeding. 



Balling gun. 

do 

....do 

....do 

do 

do 

do 

do 

do 

do 

do 



....do 

....do 

Fed with hay 

do 

....do 



Part of plant used. 



Leaves and stems 

....do 

....do 

....do 

....do 

do 

do 

do 

do 

do 

Leaves and stems with 

large proportion of 

stems. 

Leaves 

do 



Leaves and stems . 

....do 

....do 



Weteht 




of plant 




(esti- 




mated 




as green 


Remedy 


plant) 


used. 


for 100 




pounds 




of ani- 




mal. 




Pounds. 




0.140 


None 


.184 


do... 


.276 


do... 


.368 


do... 


.735 


do... 


1.102 


do... 


1.470 


do... 


2.205 


do... 


2.021 


do... 


2.113 


do... 


2.168 


do... 


1.286 


do... 


1.470 


do... 


.072 


do... 


.15 


do... 


.133 


do... 



Result. 



Not sick. 

Do. 

Do. 

Do. 

Do. 

Do. 

Do. 
Very sick. 
Not' sick. 

Do. 

Do. 



Sick. 

Do. 
Not sick. 

Do. 

Do. 



TYPICAL CASE OF SHEEP 473. 



Sheep 173 was a wether weighing 114.5 pounds at the time of 
the experiment. On July 21, 1919, between 4.05 and 4.37 p. m., it 
received by the balling gun, per 100 pounds of animal, 2.205 pounds 
of the plant, estimated as green plant. At 6.40 a. m., July 22, the 
pulse was 152, weak, but regular, and the respiration was deep. It 
seemed weak in the hind legs and staggered as it walked. 



POISONOUS PROPERTIES OF THE WHORLED MILKWEED. H 

At 7.23 a. m. it was down, throwing itself about spasmodically. 
The pupils were dilated and the animal was somewhat bloated. 
Opisthotonos was pronounced. The temperature at 6.40 a. m. was 
101° F., and at 7.33 a. m. 103.4° F. At 8.02 a. m. running move- 
ments of the legs commenced. During most of the day and through- 
out the night following the condition of the animal did not change in 
any marked degree. It had mild spasms, accompanied by convulsive 
movements of the head and jaws. At times there was distinct 
trembling. Much of the time there was a good deal of bloat. Run- 
ning movements occurred at times. The pulse was weak and the 
temperature at 2.10 p. m., and at 10.15 was as high as 105° F. The 
general condition was much like a mild case of Asclepias galioides 
poisoning. At no time were the spasms of a violent character; 
generally speaking, there was some correlation between the bloating 
and the spasmodic movements. 

During the forenoon of July 23 it was more quiet than on the 
preceding day, but it still groaned, had a weak pulse, and at 9.35 
a. m. the temperature was 104° F. At noon, while the pulse was 
still rapid, it was strong. During the afternoon the sheep drank 
water and became more quiet, though it was still bloated. 

During the forenoon of July 24 the pulse varied, being weak at 
times, but on the whole showed improvement. The sheep attempted 
to eat at 9.35 a. m. It remained down until 2.30 p. m., when it got 
on its feet. 

On July 25, while still much depressed, the sheep was improving 
steadily and both ate and drank. The temperature was normal, but 
the pulse, while strong, was still rapid. By the night of July 26 
the sheep's condition was normal. It was kept under observation 
on July 27, and was turned into pasture on July 28. 

SYMPTOMS. 

Of the three sheep poisoned by Asclepias verticillata var. geyeri, 
two, Sheep 482 and Sheep 523, were sick, and one, Sheep 473, was very 
sick. Both Sheep 482 and Sheep 523 staggered and showed general 
weakness, which, in the case of Sheep 482, was more pronounced in 
the hind legs. In this animal the respiration was labored and in 
Sheep 523 a weak pulse was noted. 

In the case of Sheep 473 all the typical symptoms of Asclepias 
galioides were noted, including weakness, especially marked in the 
hind legs, staggering, weak and rapid pulse, labored respiration 
(the expirations accompanied with groans), dilated pupils, elevated 
temperature, bloating, spasms with opisthotonos, and running move- 
ments. Spasmodic movements of the mandibles in a chewing move- 
ment were very noticeable. 



12 BULLETIN 942, U. S. DEPARTMENT OF AGRICULTURE. 

TIME REQUIRED TO PRODUCE SYMPTOMS. 

The following table shows the time that elapsed between the giv- 
ing of the plant and the appearance of symptoms : 

Table G. — Time elapsed after feeding A. verticillata var. geyeri before appt ar- 

ance of symptoms. 



Animal. 



Quantity 
fed per 

100 
pounds 
of ani- 
mal. 



Result. 



Time elapsed 

before 

symptoms 

appeared. 



Sheep 473 
Sheep 4S2 
Sheep 523 



Pounds. 
2.205 
1. 2S6 

1.47 



Very sick 

Sick 

....do.... 



Hrs. Mins 

14 10 

15 35 
20 35 



The average time before symptoms appeared was 16 hours 47 
minutes. As noted on page 6, this time, in the case of Asclejrias 
jmmila, was 16 hours and 17 minutes. In Bulletin 800, United States 
Department of Agriculture, page 34, it was shown that in the Ascle- 
pias galioides cases the average elapsed time was 14.1 hours. It is 
evident that in respect to the time elapsing between the feeding and 
the development of symptoms, the three species are practically alike. 

CONTINUATION OF SYMPTOMS. 

As in A. pumila cases, the symptoms persisted for a considerable 
length of time after their first appearance. 

In Sheep 473, symptoms continued 4 days. 

In Sheep 482, symptoms continued 2 days. 

In Sheep 523, symptoms continued 1 day. 

Sheep 473 was the only animal seriously affected, and the symptoms 

continued much longer than in the others. 



COMPARISON OF DURATION OF SYMPTOMS IN A. PUMILA, A. VERTICILLATA VAR. GEYERI, 

AND A. GALIOIDES. 

The following statement shows the time during which symptoms 
persisted in the A. galioides cases : 

Horse 126, symptoms continued 6 days. 

Cattle 750, symptoms continued 1$ days. 

Sheep 478, symptoms continued 6 hours. 

Sheep 506, symptoms continued 3 hours. 

Sheep 534, symptoms continued 1 hour. 

Sheep 542, symptoms continued 4 hours. 

Sheep 372, symptoms continued 11 hours. 

Sheep 522, symptoms continued (September 11) 3A hours. 

Sheep 522, symptoms continued (September 22) 4 hours. 

For comparative purposes the horse and cow may be disregarded. 
In fact, the horse never completely recovered, although the immediate 
symptoms of the sickness disappeared. 



POISONOUS PROPERTIES OF THE WHORLED MILKWEED. 13 

Of the sheep, 534 was only slightly sick, and 372 and 522, in both 
experiments, showed only symptoms. The average time of the sheep 
cases was between 44 and 4| hours, with a minimum of 1 hour and a 
maximum of 11 hours. The symptoms persisted longer in the more 
pronounced cases. 

It was shown on page 7 that the A. pumila cases continued from 
7^ hours to 5 days, and on page 7 that A. vt rticillata var. geyeri cases 
varied from 1 to 4 days, averaging 2 days and 8 hours. 

If sheep poisoned by A. galioides recovered they were sick only a 
few hours, while with both A. pumila and A. verticillata var. geyeri 
the symptoms continued for a prolonged period. 

Inasmuch as in all the whorled-milkweed cases the symptoms con- 
tinued longer in the more pronounced cases, and as A. galioides is 
vastly the most toxic of the three species, one would expect the 
A. galioidi s cases to continue the longest. This unexpected result is 
a matter of a good deal of interest, and there is reason to think that 
it will be explained by the detailed chemical study of these plants, 
which is now in progress. 

TOXIC DOSE. 

The leaves and stems of the plant (A. verticillata var. geyeri) were 
given by the balling gun to 10 sheep. As Asclepias galioides had been 
found to be extremely toxic, the experiments were commenced with 
small doses, which were gradually increased until results were ob- 
tained. No effect was produced until Sheep 473 became very sick 
on 2.205 pounds per hundredweight of animal. As Sheep 556 was 
not affected by 2.021 pounds, nor Sheep 546 by 2.113 pounds, it is 
a fair inference that 2.205 pounds is very close to the toxic dose. The 
smallest toxic dose of Asclepias galioides is 0.22 pound, while the 
smallest toxic dose of Asclepias pumila is 0.787 pound. Asclepias 
verticillata var. geyeri, then, is about one-third as toxic as A. pumila 
and about one-tenth as toxic as A. galioides when leaves and stems 
are fed. 

In feeding the leaves of the plant by the balling gun the smallest 
dose was 1.286 pounds. The smallest toxic dose of A. galioides leaves 
fed in the same way was 0.138 pound, so that in this case the A. 
galioides was about nine times as toxic as the A. verticillata var. 
geyeri. 

COMPARATIVE TOXICITY OF STEMS AND LEAVES. 

It may be noted that, as shown in the preceding paragraph, when 
leaves and stems are fed together the toxic dose is 2.2 pounds, while 
with leaves alone it is 1.378 pounds. This difference, of course, is 
due to the greater toxicity of the leaves. This is a matter of a great 
deal of interest, for extended experiments on A. galioides carried 
on since the publication of Bulletin 800 have conclusively shown a 



14 BULLETIN &42, U. S. DEPARTMENT OF AGRICULTURE. 

similar relation in this plant. It follows that the losses by the 
whorled milkweeds are for the most part caused by eating the leaves 
rather than the stems. 

SUMMARY. 

Closely allied to the extremely poisonous whorled milkweed Ascle- 
pias galioides are two species, A. pumila, growing in the plains 
region east of the Rocky Mountains, and A. verticillata var. geyeri, 
growing in the eastern United States. 

These two species produce in animals symptoms and pathological 
results closely resembling those produced by A. galioides. 

As compared with A. galioides, A. pumila is about one- third as 
toxic and the Missouri Valley species (-4. verticillata var. geyeri) 
about one-tenth as toxic. 

As stock-poisoning plants these last two species have no history, 
but there is reason to think that if grazing animals were closely con- 
fined to them injurious results would follow. 



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